Expression usage - Amazon IoT Events
Writing Amazon IoT Events expressions
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Expression usage

You can specify values in a detector model in the following ways:

  • Enter supported expressions in the Amazon IoT Events console.

  • Pass the expressions to the Amazon IoT Events APIs as parameters.

Expressions support literals, operators, functions, references, and substitution templates.

Important

Your expressions must reference a integer, decimal, string, or Boolean value.

Writing Amazon IoT Events expressions

See the following examples to help you write your Amazon IoT Events expressions:

Literal

For literal values, the expressions must contain single quotes. A Boolean value must be either true or false.

'123'        # Integer
'123.12'     # Decimal
'hello'      # String
'true'       # Boolean
Reference

For references, you must specify either variables or input values.

  • The following input references a decimal number, 10.01.

    $input.GreenhouseInput.temperature

  • The following variable references a string, Greenhouse Temperature Table.

    $variable.TableName
Substitution template

For a substitution template, you must use ${}, and the template must be in single quotes. A substitution template can also contain a combination of literals, operators, functions, references, and substitution templates.

  • The evaluated result of the following expression is a string, 50.018 in Fahrenheit.

    '${$input.GreenhouseInput.temperature * 9 / 5 + 32} in Fahrenheit'

  • The evaluated result of the following expression is a string, {\"sensor_id\":\"Sensor_1\",\"temperature\":\"50.018\"}.

    '{\"sensor_id\":\"${$input.GreenhouseInput.sensors[0].sensor1}\",\"temperature\":\"${$input.GreenhouseInput.temperature*9/5+32}\"}'
String concatenation

For a string concatenation, you must use +. A string concatenation can also contain a combination of literals, operators, functions, references, and substitution templates.

  • The evaluated result of the following expression is a string, Greenhouse Temperature Table 2000-01-01.

    'Greenhouse Temperature Table ' + $input.GreenhouseInput.date